[Raak] Precious stones? NO *sustained applause from the audience*
[CdM] The word "stone" IS on the card *mounting excitement from audience*
[Inkspot] Back to Greek and Roman times? YES
[rab] Arthurian connection? NOT THAT I'M AWARE OF
[CdM] Alchemists' stone? YES. The words on the card were "Philosopher's Stone", and I have to say I'm very upset that Tuj never popped up with his normal question! I got in a bit of a tizzy over the legend/myth questions. To my knowledge, the philosopher's stone doesn't appear in a particular myth or legend or in what is conventionally called mythology (i.e. of the Greek and Roman variety), but one could call it a mythical or legendary object, so a hard one to answer helpfully. * transmutes baton into finest gold and hands to CdM*

Global Warming? No.

Visible? Yes.
Human Construct? Yes.
Fictional? No, although there are a few connections to works of fiction.

Symbol? I think the most helpful answer is no.